Radiation shielding structure composition

ABSTRACT

Radiation structures formed from a composition including calcium silicate, magnesium or calcium oxides and an acid phosphate are provided. The composition may also include fly ash or kaolin.

RELATED APPLICATIONS

This application is a continuation application of U.S. application Ser. No. 12/572,795, filed Oct. 2, 2009, which claims priority to U.S. Provisional Application Ser. No. 61/102,997, filed Oct. 6, 2008, the contents of which are hereby incorporated herein by reference in their entireties.

FIELD AND BACKGROUND OF THE INVENTION

The present invention relates generally to a composition useful in radiation shielding applications.

The use of radiation shielding structures is common, particularly in the nuclear technology field and in any radiation producing facility. Exemplary radiation sources include cosmic rays, x-rays in medical facilities, nuclear reactors, cathode ray tubes (e.g. TV and computer monitors) and the like. Radiation doses are carefully monitored in a wide variety of settings, and there are a number of regulatory standards for human exposure levels. Radiation shielding is also important for limiting exposure of sensitive equipment to radiation. For example, protection of a nuclear reaction vessel from gamma rays. Another example, is the protection of other medical devices from radiation from a medial device that emits radiation.

Concrete or cement is often a candidate material for use in radiation shielding. For example, U.S. Pat. No. 5,786,611 proposes containers for storing spent nuclear wastes. The containers comprise concrete with stable uranium oxide aggregate and a neutron absorbing material such as B₂O₃, HfO₃ or Gd₂O₃. U.S. Pat. No. 4,727,257 proposes a radiation shielding composition comprising an aggregate-containing cement based mortar wherein the aggregate comprises floated gelata and a boron mineral. U.S. Publication No. 2002/0165082 proposes a phosphate ceramic radiation shielding composition comprises a magnesium, potassium and phosphorous binder, and means for dissipating heat such as B₄C, Bi₂O₃, Fe₂O₃, Fe₃O₄, Pb metal and lead.

There is, however, a need for compositions for radiation shielding structures which are less expensive and less dependent on heavy metals while providing acceptable levels of shielding from radiation.

SUMMARY OF THE INVENTION

Radiation shielding structures are widely used for shielding of nuclear power plants, particle accelerators, research reactors, laboratory equipment, and radiation and x-ray medical facilities. An important aspect is selecting the specific shielding structure as the required attenuation coefficient or reduction factor. The Linear Attenuation Coefficient (μ) is dependent on the density of the shielding material. To obviate the effects of variations in the density of a material, the linear attenuation coefficient is expressed as a mass attenuation coefficient (μ/ρ) cm²g⁻¹. It is the direct measure of the effectiveness of a shielding material based upon unit mass of a material.

To this end, the present invention provides a radiation shielding structure composition comprising calcium silicate, magnesium oxide and an acid phosphate. The radiation shielding structure has an improved attenuation coefficient as compared to ordinary concrete based on photon energies of 0.662 MeV (5 μCi Cs-137 source) and 1.173 MeV (1 μCi Co-60 source).

In another embodiment, the present invention provides a radiation shielding structure composition comprising magnesium or calcium oxide, an acid phosphate and fly ash and having an improved attenuation coefficient as compared to ordinary concrete based on photon energies of 0.662 MeV (5 μCi Cs-137 source) and 1.173 MeV (1 μCi Co-60 source).

In still another embodiment, the present invention provides a radiation curing structure composition comprising magnesium or calcium oxide, an acid phosphate and kaolin and having an improved attenuation coefficient as compared to ordinary concrete based on photon energies of 0.662 MeV (5 μCi Cs-137 source) and 1.173 MeV (1 μCi Co-60 source).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph of attenuation coefficients for the radiation shielding structure compositions of Examples 1-6 and ordinary concrete (“OC”) for 0.66 MeV photon energy using a 5 mCi Cs-137 source.

FIG. 2 is a graph of attenuation coefficients for the radiation shielding structure compositions of Examples 1-6 and ordinary concrete (“OC”) for 1.173 MeV photon energy using a 1 μCi Co-60 source.

DETAILED DESCRIPTION OF THE INVENTION

The foregoing and other aspects of the present invention will now be described in more detail with respect to other embodiments described herein. It should be appreciated that the invention can be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

The terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used in the description of the embodiments of the invention and the appended claims, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. Also, as used herein, “and/or” refers to and encompasses any and all possible combinations of one or more of the associated listed items. Furthermore, the term “about,” as used herein when referring to a measurable value such as an amount of a compound, dose, time, temperature, and the like, is meant to encompass variations of 20 percent, 10 percent, 5 percent, 1 percent, 0.5 percent, or even 0.1 percent of the specified amount. Unless otherwise defined, all terms, including technical and scientific terms used in the description, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

The radiation shielding structure comprises calcium silicate (wollastonite), magnesium oxide and an acid phosphate. In one embodiment, the composition comprises about 15 to 40 percent by weight calcium silicate, about 10 to 35 percent by weight magnesium oxide and about 25 to 45 percent by weight acid phosphate. Such a composition optionally may include kaolin or fly ash at a 0.1 to 40 percent by weight level.

In another embodiment the radiation shielding structure comprises magnesium or calcium oxide, an acid phosphate and fly ash. In one embodiment, the structure comprises 15 to 40 percent by weight calcined magnesium or calcium oxide, 25 to 55 percent by weight acid phosphate and 20 to 40 percent by weight fly ash.

In another embodiment, the radiation shielding structure comprises a magnesium or calcium oxide, an acid phosphate and kaolin. In one embodiment, the structure comprises 15 to 40 percent by weight calcined magnesium or calcium oxide, 20 to 55 percent by weight acid phosphate and 5 to 25 percent by weight kaolin

Exemplary acid phosphates include monopotassium phosphate, magnesium phosphate, sodium phosphate, aluminum phosphate, ammonium phosphate, iron phosphate, zinc phosphate, and combinations thereof. In the embodiments above, the acid phosphate may be monopotassium phosphate.

Suitable additives may be mixed with the radiation shielding structure composition and typically the amounts added may be from about 0.1 to about 30 percent by weight. Exemplary additives include flame retardants, vermiculite, perlite, fibers, emulsifiers, deflocculates, sequestrates, granular additives, coarse aggregates such as stone and sand, chemical additives such as boric acid, accelerators (e.g., Accelguard available from The Euclid Chemical Company, Cleveland, Ohio) colorants and pigments, fillers, aggregates, borax, silica materials, iron oxides, bonding adhesives (e.g., Eucopoxy Resin and Eucoweld available from The Euclid Chemical Company, Cleveland, Ohio, Flexcon, and Con-bond) plasticizers, hardeners (e.g., Euco Diamond Hard available from The Euclid Chemical Company, Cleveland, Ohio), patching polymers (e.g., Eucorapid patch available from The Euclid Chemical Company, Cleveland, Ohio), micro silica fume (e.g., Eucoshot available from The Euclid Chemical Company, Cleveland, Ohio), setting retarders, surface softeners, and kaolins, curing compounds (e.g., Brownstone CS), water reducers (e.g., Accelguard, Eucon AC), and air entrainers (e.g., AEA and Air Mix).

Alternatively, neutron absorbers also may be added to the radiation shielding structure. Exemplary neutron absorbers include heavy metals and heavy metal compounds such as boron, B₂O₃, HfO₃, Gd₂O₃, iron oxides, lead, and the like.

Alternatively, various reinforcement may be included in the composition or the composition may be applied to the reinforcement. Exemplary reinforcement includes steel (e.g. rebar), other metals (e.g., lead) carbon, glass, stone, basalt, and the like in fiber, particulate and/or fabric/mat form.

The radiation shielding structure composition can be mixed as a slurry and sprayed on an existing surface or substrate to improve the attenuation coefficient of that surface or the slurry can be sprayed, extruded, molded, and the like into a predetermined shape. Suitable structures include shielding for nuclear power plants, particle accelerators, research reactors, x-ray equipment, radiation equipment, and the like. Other structures include transport and storage vessels for containing waste capable of emitting harmful radiation such as described in U.S. Ser. No. 12/572,812, filed Oct. 2, 2009, the disclosure of which is incorporated herein by reference in its entirety.

The following examples are merely illustrative of the invention, and are not limiting thereon.

EXAMPLES

Examples 1-6 were formulated as follows:

Example 1

Magnesium Oxide 23% Monopotassium Phosphate 23% Fly Ash 21% Sand 33% The sample tested had a thickness of 0.50 inches.

Example 2

Magnesium Oxide 20% Monopotassium Phosphate 23% Calcium Silicate 24% Sand 33% The sample tested had a thickness of 1.25 inches.

Example 3

Example 1 was repeated with salt water. The sample tested had a thickness of 2.00 inches.

Example 4

Magnesium Oxide 23% Monopotassium Phosphate 23% Fly Ash 11% Kaolin 10% Sand 33% The sample tested had a thickness of 0.75 inches.

Example 5

Magnesium Oxide 30% Monopotassium Phosphate 34% Calcium Silicate 36% The sample tested had a thickness of 0.50 inches.

Example 6

Magnesium Oxide 30% Monopotassium Phosphate 31% Fly Ash 28% Sodium Bicarbonate 10% The sample tested had a thickness of 1.00 inches.

Example 7

Example 1 was repeated and the sample tested had a thickness of 1.00 inches. The testing was conducted using a method for measuring attenuation coefficients developed by North Carolina State University.

As can be seen from FIGS. 1 and 2, the formulations for Examples 1-6 have significantly improved attenuation coefficients as compared to ordinary concrete.

Example 8

A formulation as follows was prepared.

Magnesium Oxide 34% Monopotassium Phosphate 31% Fly Ash 17% Kaolin 15%

Example 9

Magnesium Oxide 34% Monopotassium Phosphate 31% Fly Ash 17% Kaolin 15% Sand 30%

Having thus described certain embodiments of the present invention, it is to be understood that the invention defined by the appended claims is not to be limited by particular details set forth in the above description as many apparent variations thereof are possible without departing from the spirit or scope thereof as hereinafter claimed. 

What is claimed is:
 1. A radiation shielding structure composition comprising 10 to 40 percent by weight calcium silicate, 10 to 35 percent by weight magnesium oxide, and 15 to 45 percent by weight acid phosphate and having an improved attenuation coefficient as compared to ordinary concrete based on photon energies of 0.662 MeV (5 μCi Cs-137 source) and 1.173 MeV (1 μCi Co-60 source).
 2. The radiation shielding structure composition of claim 1, wherein the acid phosphate is monopotassium phosphate.
 3. The radiation shielding structure composition of claim 1, further comprising fly ash or kaolin or both.
 4. A radiation shielding structure comprising the radiation shielding structure composition of claim 1 sprayed onto a substrate or formed into predetermined structure.
 5. A method of shielding a structure or substrate from radiation, the method comprising applying a composition comprising 10 to 40 percent by weight calcium silicate, 10 to 35 percent by weight magnesium oxide, and 15 to 45 percent by weight acid phosphate to the structure or substrate. 